Cookies

We use cookies to ensure that we give you the best experience on our website. By continuing to browse this repository, you give consent for essential cookies to be used. You can read more about our Privacy and Cookie Policy.


Durham Research Online
You are in:

A mechanism for stimulating AGN feedback by lifting gas in massive galaxies.

McNamara, B. R. and Russell, H. R. and Nulsen, P. E. J. and Hogan, M. T. and Fabian, A. C. and Pulido, F. and Edge, A. C. (2016) 'A mechanism for stimulating AGN feedback by lifting gas in massive galaxies.', Astrophysical journal., 830 (2). p. 79.

Abstract

Observation shows that nebular emission, molecular gas, and young stars in giant galaxies are associated with rising X-ray bubbles inflated by radio jets launched from nuclear black holes. We propose a model where molecular clouds condense from low-entropy gas caught in the updraft of rising X-ray bubbles. The low-entropy gas becomes thermally unstable when it is lifted to an altitude where its cooling time is shorter than the time required to fall to its equilibrium location in the galaxy, i.e., ${t}_{{\rm{c}}}/{t}_{{\rm{I}}}\lesssim 1$. The infall speed of a cloud is bounded by the lesser of its free-fall and terminal speeds, so that the infall time here can exceed the free-fall time by a significant factor. This mechanism is motivated by Atacama Large Millimeter Array observations revealing molecular clouds lying in the wakes of rising X-ray bubbles with velocities well below their free-fall speeds. Our mechanism would provide cold gas needed to fuel a feedback loop while stabilizing the atmosphere on larger scales. The observed cooling time threshold of $\sim 5\times {10}^{8}\,\mathrm{yr}$—the clear-cut signature of thermal instability and the onset of nebular emission and star formation—may result from the limited ability of radio bubbles to lift low-entropy gas to altitudes where thermal instabilities can ensue. Outflowing molecular clouds are unlikely to escape, but instead return to the central galaxy in a circulating flow. We contrast our mechanism to precipitation models where the minimum value of ${t}_{{\rm{c}}}/{t}_{{\rm{ff}}}\lesssim 10$ triggers thermal instability, which we find to be inconsistent with observation.

Item Type:Article
Full text:(VoR) Version of Record
Download PDF
(1012Kb)
Status:Peer-reviewed
Publisher Web site:https://doi.org/10.3847/0004-637X/830/2/79
Publisher statement:© 2016. The American Astronomical Society. All rights reserved.
Date accepted:20 July 2016
Date deposited:04 May 2017
Date of first online publication:14 October 2016
Date first made open access:04 May 2017

Save or Share this output

Export:
Export
Look up in GoogleScholar